The Effects of Labor on the Biomechanical Properties of the Femora and the Humeri in the 19th and 20th Centuries
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Bone is an adaptive tissue that can change in shape and size throughout the course of life due to loading regime through the modeling and remodeling process. Therefore, the cross-sectional geometry (CSG) of long bone shafts provides a generalized measure of the loading that occurred during life. The purpose of this study is to investigate differences in long bone strength and shape between manual and non-manual labor workers in the 19th and 20th centuries and examine if there is any secular change occurring between the 19th and 20th century individuals. This research was completed by taking high-resolution x-ray computed tomography (HRXCT) scans of the left femur and both humeri for each individual. The cross-sectional geometric properties were analyzed, and an ANOVA was run to test for significant differences between size, shape, and robusticity between the manual and non-manual labor workers. The results showed that the humeri of manual labor workers are significantly more robust than non-manual labor workers in the 20th century sample. However, the femora were significantly larger in the non-manual labor workers in the 20th century sample. In the 19th century sample, there were no significant differences in the size, shape, or robusticity of the humeri or femora between manual and non-manual labor workers. Secular change was also observed in the femur, with the 20th century sample having larger and more round femora in comparison to the 19th century individuals.